In a type of fruit fly the brown body colour allele is dominant to the black body colour allele. A male fruit fly heterozygous for body colour and a female fruit fly heterozygous for body colour were allowed to mate, producing offspring. What is the ratio, in its simplest form, of the maximum number of genotypes in the offspring to the maximum number of phenotypes in the offspring?

Answer:

25) C

Let dominant allele be B
Let recessive allele be b

Genotype of male fly = Bb
Genotype of female fly = Bb

Simple monohybrid cross produces 3 genotypes: BB, Bb and bb (You should know how to do the cross).

Number of phenotypes is only 2. BB and Bb produce brown flies whilst bb produces black flies.

Max number of genotypes : Max number of phenotypes = 3 : 2

So C is the answer.